\begin{tikzpicture}

\definecolor{darkgray176}{RGB}{176,176,176}

\begin{groupplot}[group style={group size=1 by 2}]
\nextgroupplot[
tick align=outside,
tick pos=left,
title={Taylor--Green Vortex},
x grid style={darkgray176},
xlabel={x},
xmin=0, xmax=6.2831853,
xtick style={color=black},
y grid style={darkgray176},
ylabel={y},
ymin=0, ymax=6.2831853,
ytick style={color=black}
]
\addplot graphics [includegraphics cmd=\pgfimage,xmin=0, xmax=6.2831853, ymin=0, ymax=6.2831853] {tmp-000.png};

\nextgroupplot[
tick align=outside,
tick pos=left,
x grid style={darkgray176},
xlabel={x},
xmin=0, xmax=6.2831853,
xtick style={color=black},
y grid style={darkgray176},
ylabel={y},
ymin=0, ymax=6.2831853,
ytick style={color=black}
]
\addplot graphics [includegraphics cmd=\pgfimage,xmin=0, xmax=6.2831853, ymin=0, ymax=6.2831853] {tmp-001.png};
\end{groupplot}

\end{tikzpicture}
